Nashville among U.S. cities sinking due to this invisible threat, study says
That's what a new study from the British journal Nature Cities reported on May 8. Nashville, along with 27 other cities around the United States.
In every city studied, at least 20% of the urban area is sinking. Plus, in 25 of the 28 cities studied, at least 65% is sinking.
The reason behind the sinking ground is called subsidence, an often invisible threat that exists most often when water, oil, natural gas, or mineral resources are removed from the ground by pumping, fracking, or mining activities. Subsidence can also be caused by natural events like earthquakes, sinkholes, erosion, soil compaction and more, according to the National Ocean Association.
Most often, extracting groundwater can be the most common reason for subsidence.
The gradual subsidence may impact the structural integrity of buildings, roads, bridges and dams, according to the study.
"One of the most harmful yet less visible effects of urban land subsidence is the potential damage to buildings, foundations and infrastructure, primarily caused by differential land motion," the study said.
Generally, according to a statement from the Lamont-Doherty Earth Observatory — one of the study's authors, it happens as water is withdrawn from aquifers made up of fine-grained sediments; unless the aquifer is replenished, the pore spaces formerly occupied by water can eventually collapse, leading to compaction below, and sinkage at the surface.
Nashville, along with New York, Indianapolis, Chicago, Philadelphia, Denver and Portland, is among the cities subsiding at a rate of 1 to 3 millimeters per year due to both human-derived and natural forces.
"In particular, the weight of the towering ice sheet that occupied much of interior North America until about 20,000 years ago made the land along its edges bulge upward, somewhat like when one squeezes air from one part of a balloon to another," said the Lamont-Doherty Earth Observatory.
The fastest sinking city is Houston, the study uncovered. Houston saw more than 40% of its area dropping more than 5 millimeters (about 1/5 inch) per year, and 12% sinking at twice that rate.
No. In fact, Memphis is one of three cities identified in the study that appears to have a small uplift of around 0.1 millimeters. This doesn't mean that the city is rising per se, but more of an indication of its current stability, study lead author Leonard Ohenhen of the Lamont-Doherty Earth Observatory told USA TODAY.
San Jose and Jacksonville are the other two U.S. cities that were uplifted, marked by light green dots on the map.
Knoxville was not included in the study.
Only the most populous 28 U.S. cities were included in the British journal Nature Cities' published study of land subsidence risk.
Subsidence is not something that can be immediately reversed, however, the study does recommend ways to minimize the impacts on affected cities.
The study highlighted the importance of monitoring land subsidence as a part of urban planning to prevent worsening infrastructure risks.
"Regardless of the pathway a city chooses, any effective mitigation and adaptation effort must be targeted to the dominant subsidence driver in each city, proportional to local vulnerabilities, and incorporate a multifaceted approach," the study said.
Techniques like groundwater management and long-term monitoring frameworks are a key way to combat land subsidence.
USA TODAY reporter Doyle Rice contributed to this report.
This article originally appeared on Nashville Tennessean: Nashville among U.S. cities sinking, according to new study
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